Role of MiR-148b in angiogenesis and endothelial cell plasticity

Abstract

Endothelial cells (ECs) have a well-established role in the maintenance of vascular physiology. Moreover, ECs participate in many physiological processes such as angiogenesis, blood homeostasis, inflammatory response, lipid metabolism and many more. Angiogenesis is one of the most studied functions of endothelium, where ECs participate in the formation of the new blood vessels. Additionally, ECs can also exhibit a form of plasticity called endothelial-to-mesenchymal transition (EndMT), which is characterized by the loss of endothelial-specific morphology and markers and acquisition of mesenchymal-like phenotype. Both angiogenesis and EndMT can be regulated by physiological cues, such as inflammation and haemodynamic forces, as well as number of molecular stimuli, such as TGF-β. Interestingly, recent evidence suggests that angiogenesis and EndMT can be orchestrated by miRNAs. This thesis aims to address the hypothesis that miR-148b is a modulator of angiogenesis and endothelial cell plasticity in the form of EndMT. The preliminary high-throughput miRNA screen has identified miR-148b as a strong enhancer of HUVEC proliferation. Subsequent bioinformatic analysis and validation demonstrated that TGFB2 and SMAD2 are direct targets of miR-148b in ECs. Further experiments using gain- and loss-of-function approaches demonstrated that miR-148b regulates EC function. Specifically, overexpression of miR-148b enhanced EC migration, proliferation and in vitro angiogenesis, whereas its inhibition promoted EndMT, decreasing the expression of CD31 and VE-Cadherin and elevating collagen 1. Furthermore, inflammatory cytokine challenge decreased miR-148b levels in ECs, promoting EndMT, via upregulation of SMAD2, and enhancing reactive oxygen species production, all of which were abrogated by exogenous miR- 148b. Finally, in a mouse model of skin wound healing, delivery of miR-148b mimics promoted wound angiogenesis and accelerated wound closure. In contrast, inhibition of miR-148b enhanced EndMT in wounds impairing wound closure, which is reverted by SMAD2 silencing. Together, the data in this thesis supports the hypothesis that miR-148b regulates angiogenesis and endothelial cell plasticity, and provides the evidence that miR-148b upregulation enhances both in vitro and in vivo angiogenesis, while its knockdown promotes EndMT. This thesis demonstrates for the first time that miR-148b could be a key factor controlling EndMT and vascularization, thus opening a new avenue for therapeutic application of miR-148b in diseases that require vascular and tissue repair.